Granulomatous appendicitis and the appendix in idiopathic inflammatory bowel disease.

Granulomatous appendicitis is a rare condition, accounting for less than 2% of all cases of appendicitis. The initial belief that it represented a manifestation of Crohn's disease is incorrect in the great majority of cases, as only 5-10% of patients with granulomatous appendicitis develop Crohn's disease elsewhere in their gastrointestinal tract. The remaining etiologies are diverse. Unusual causes include sarcoidosis, foreign body reaction, and infection by mycobacteria, fungi, or parasites. These conditions combined explain less than 10% of cases. More recently, two etiologies have been recognized that potentially account for most of the previous "idiopathic" cases of granulomatous appendicitis. The first is infection by pathogenic Yersinia species, now demonstrated in approximately 25% of cases. The second cause may be the most common of all, namely subacute/recurrent appendicitis with interval appendectomy. This condition likely produces a granulomatous reaction in relation to a protracted secondary inflammatory response to appendicitis and temporizing measures to delay appendectomy, such as antibiotic therapy. Thus, granulomatous appendicitis only rarely represents a manifestation of Crohn's disease. Rather, the overwhelming majority of patients with this condition are cured by appendectomy alone. The appendix, however, can be involved by idiopathic inflammatory bowel disease, both Crohn's disease and ulcerative colitis. It can be involved by ulcerative colitis in patients with distal colonic involvement and sparing of the intervening colonic segment, a phenomenon known as the appendiceal "skip lesion" or "cecal patch" and this pattern of involvement does not necessarily indicate Crohn's disease. Interestingly, appendectomy has been shown to provide some protection against developing inflammatory bowel disease and in reducing its severity if performed before the onset of disease.